Swabbing apparatus of the relevant type usually comprises a hollow core for receiving lifting apparatus such as the mandrel of a wireline workover unit. In conventional swabbing apparatus a plurality of working lips, which are made of elastomeric material and which all have the same fluid load carrying capacity, are molded onto the core. These lips are capable of carrying only a relatively narrow range of fluid loads; thus, the entire swabbing apparatus is useful only over the same narrow range of fluid loads. This fluid load carrying capacity may be broadened slightly by adding support lips beneath the working lips. Such an approach is exemplified by Read U.S. Pat. No. 3,352,212. For swabbing the various ranges of fluid loads that are encountered downhole, a particular swabbing apparatus that is designed for each such particular range of fluid loads, must be used. The particular range of fluid loads that will be encountered by a swabbing apparatus at a job site will not be definitely known by the workover operator and he must consequently guess at which particular swabbing apparatus would be best to use. The fact that each swabbing apparatus is useful over only a narrow range of fluid loads is disadvantageous. Since the well site is usually in a location remote from a source of supply, the workover operator must have in his truck inventory swabbing apparatuses of several different diameters to cover the various casing or tubing diameters that will be encountered, with several swabbing apparatuses of different load ranges for each such diameter. This adds up to the necessity for a large inventory of swabbing apparatuses. A swabbing apparatus having a relatively broad range of load carrying capacities would alleviate the problems discussed above. Although some efforts have been made to provide swabbing apparatuses having a relatively broad range of load carrying capacities, the resulting swabbing apparatus has not proved to be entirely satisfactory.
It is accordingly the objective of this invention to provide an improved swabbing apparatus that has a relatively broad range of fluid load carrying capacities.